1. Technical Field
This invention relates to the art of making permanent magnets, and more particularly to the art of making cobalt-based magnets.
2. Discussion of the Prior Art
The first major use of cobalt in the making of permanent magnets occurred about 1969 when used as a base in conjunction with rare earths to attain an energy product material higher than anything attained with the best ALNICO alloys for ferrite magnets. Such cobalt/rare earth magnets possessed strong anisotropism and large coercivities (see U.S. Pat. Nos. 4,081,297; 4,090,892; 4,131,495; 4,213,803; 4,369,075; and articles listed in the Appendix).
Due to the difficulty of obtaining cobalt at reasonable cost, this advancement was overshadowed by the development of stabilized iron-based rare earth magnet alloys which attained many magnetic properties equal to or greater than that of cobalt-based rare earth magnets. Optimization of such iron-based rare earth magnets has continued throughout the 1980's, including resubstitution of cobalt for iron (see Fuerst, C. D. and Herbst, J. F. (1988), "Hard Magnetic Properties of Nd--C--B Materials", Journal of Applied Physics. Vol. 64, No. 3, page 1332; and Fuerst, C. D., Herbst, J. F., and Pinkerton, F. E. (1988), "Magnetic Hardening of Pr.sub.2 Co.sub.14 B", Journal of Applied Physics. Vol. 64, No. 10, page 5556) to stabilize magnetic properties at higher temperatures, but did so with significant degradation of the properties of the rare earth system.
With changing economics of raw material supply, including an increase in the abundance of cobalt and an increase in the price of rare earths, it has recently become practical to deploy cobalt as a predominant ingredient of permanent magnets without the presence of rare earths. Applicants are unaware of any prior art that has investigated rare earth free cobalt-based permanent magnets except for an active basic research program carried out at the Massachusetts Institute of Technology, Cambridge, Mass., directed to cobalt/boron alloys as evidenced by the article "Magnetic Moment Suppression in Rapidly Solidified Co--TE--B Alloys", by A. M. Ghemawat et al, Journal of Applied Physics, Vol. 63, No. 8, pages 3388-3390 (Apr. 15, 1988). This latter work merely observed that the magnetic moment decreased by adding a transition element (TE) to a cobalt/boron or cobalt/copper alloy. The authors reasoned that the TE and boron or copper competed for hybridization of the cobalt state to result in such decrease.
Contrary to this MIT work, an investigation was undertaken in accordance with this invention to see if a stabilized cobalt-based transition metal alloy could be processed to result in significant enhancement of its magnetic properties while possessing high temperature stability and desirable corrosion resistance.